A running engine of a motor vehicle produces noise waves whose carrying medium is the pulsating stream of exhaust gases guided by a pipe from the engine to ambient environment. It is known that the intensity of noise decreases in proportion to the increase of losses. Such loss can rise due to absorption of noise energy, for which various filling materials can be used, such as glass wool, or resonators arranged along the stream of exhaust gases. Also the use of perforated walls for the passage of a noise wave is known, or repeated contractions and expansions, or possibly changes of direction of at least a part of the main stream of exhaust gases, further reflections of noise waves and elongation of the path of exhaust gases, or their cooling. The resulting effect of the silencer depends also upon the ratio of the silencer volume to the working volume of the engine cylinders. The present day design trends of silencers of exhaust gases suggest various combinations and respective arrangements of the mentioned suppressing means. For instance a solution is known according to patent CZ 286939 comprising an elongated case with internal space divided by parallel partitions and partitions with gaps at their ends in alternating arrangement, or having openings in their central part, creating a plurality of chambers with increasing volume in the stream direction of exhaust gases. Such solution can suppress the noise waves of exhaust gases, however, by far not meeting the present day requirements relating to their residual intensity.
Yet another solution is known according to CZ PV 1993-2264 that was adversely terminated after its disclosure. It comprises a chamber accommodating a perforated tube provided with a set of small holes and a plurality of rows of larger holes. The perforated tube contains a reflective hollow body created by a pair of cones with a gap between their broad ends. The end of the perforated tube carries a number of larger holes. This solution ensures higher efficiency of noise waves suppression by using an inserted perforated tube with larger holes and smaller ones through which parts of the exhaust gases pass at different distances into the outer zone of the chamber where their mixing and whirling takes place, whereupon they return to the perforated tube. The present day requirements regarding the size of suppression, however, have not been met by this solution, either.
A further embodiment of a silencer is offered by EP 1 477 642 describing a few silencer alternatives comprising, in an elongated case, an input tube penetrating roughly to ⅔ length from one side and an outlet tube penetrating to about ⅔ length from the opposite side. At least one of them is provided by a set of openings. Openings are also created in the carrying partitions of these tubes. This solution ensuring, in the remaining ⅓ length, a compression of stream of exhaust gases, on the one hand side, and the change of their direction and returning to the system of holes in the carrying partition, on the other hand, induces a change of their velocity and turbulence. A higher intensity of suppression of the noise waves in this embodiment is also ensured by a part of the exhaust gases entering into the outlet tube, where the main part of the stream of exhaust gases escaping to free air gets twirled. Nevertheless, such solution does not achieve the intensity of noise wave suppression, either, as required in the present day motor vehicle.